1. Field of Invention
The present invention relates to power conversion, and more particularly, to current sensing in a power converter.
2. Description of Related Art
Power converters are essential for many modem electronic devices. Among other capabilities, power converters can adjust voltage level downward (buck converter) or adjust voltage level upward (boost converter). Power converters may also convert from alternating current (AC) power to direct current (DC) power, or vice versa. Power converters are typically implemented using one or more switching devices, such as transistors, which are turned on and off to deliver power to the output of the converter. Control circuitry is provided to regulate the turning on and off of the switching devices, and thus, these converters are known as “switching regulators” or “switching converters.” The power converters may also include one or more capacitors or inductors for alternately storing and outputting energy.
In a power converter, accurately sensing the output current can be of great importance. For example, in current-mode controllers, the output current can be used as the feedback input to the controller, making it an essential part of the control loop. Information about the output current can also be used for protection, for example, to protect the output inductor from saturation or to prevent overheating of the power devices. As power converters run at higher frequencies to reduce passive sizes and increase transient response time, sensing or detecting the output current becomes more and more challenging.
In particular, the current sensing must be accurate, fast, and not introduce or cause transient dependant error signals. That is, the current sensing accuracy needs to be preserved over variations in device process, supply voltage, and temperature (PVT). The sensing scheme should be fast—i.e. wide band in order keep up with the higher operating frequency of the modern power converters. Finally, because the power switch in a power converter turns on and off every clock cycle, the sensing circuitry needs to turn on and off equally fast, and behave well doing so without introducing transient dependant error signals.